


For Research (W.D. Gaster/Reader)

by EsperAqua



Category: Undertale (Video Game)
Genre: Adult Content, Arousal, Blow Jobs, Body Exploration, Budding Love, Choking, Control, Control Issues, Cunnilingus, Curiosity, Ecto-Penis, Exploration, F/M, Fear, Fellatio, First Time, Good W. D. Gaster, Hair Pulling, Humiliation, Light Bondage, Magic Cock, Multiple Orgasms, Oral Sex, Pre-Chara, Pre-Core, Reader Is Not Frisk, Science Experiments, Self-Mutilation, Sex, Soul Sex, Vaginal Fingering, anger issues, bone punching, magic bindings, mentioned pain
Language: English
Status: Completed
Published: 2016-03-31
Updated: 2016-07-09
Packaged: 2018-05-30 08:19:55
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 6
Words: 14,864
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6416041
Author URL: https://archiveofourown.org/users/EsperAqua/pseuds/EsperAqua
Summary: <blockquote class="userstuff">
              <p>Dr. W.D. Gaster has been wanting to perform some research on the external anatomy of a human for quite some time, but no one has been around for him to do so. Luckily for Gaster the human that had recently fallen to the underground is willing to permit him to do conduct his research in the True Lab... However as he begins to explore and document her body, he begins to find his own curiosities begin to over take him.</p>
            </blockquote>





	1. The Meeting

**Author's Note:**

> This is my first fanfic ever, let alone adult fanfic, so I hope my readers will understand that :) If this get a lot of positive feedback I will write a follow up!
> 
> Also, if you are interested, follow my Tumblr at http://esperaqua.tumblr.com/, it's where I post my Undertale Cosplay photos (both SFW and NSFW), and chapter updates!

**Summary for the Chapter:**

> Dr. W.D. Gaster has been wanting to perform some research on the external anatomy of a human for quite some time, but no one has been around for him to do so. Luckily for Gaster, he is about to find one...

It had been years since the last human had fallen to the Underground, maybe well over a decade. W.D. Gaster was about to give up and move on with his human research papers, but then he heard wind that one was recently spotted living in a remote part of the Underground called Snowdin from one of his more gossipy "Followers". Snowdin was vastly uninhabited save for a building or two, and he wondered how the human could have possibly been faring given then nature of their circumstances in such a frozen place. Normally he would send one of his "Followers" out to fetch him human samples in various places, mostly the Dump, but this time out of sheer curiosity Gaster decided to take the rest of the day off and visit the tiny town to see if the rumors really were true.  


Upon his arrival at the Snowdin boat ramp, Gaster looked around the vastly white landscape with a frown. He highly disliked the stark bright white nature of this place, and had hoped to see the human in question as soon as possible so he could get back into his dimly lit laboratory, in which he felt the most at home. It didn't take him long to find the first monster to question about the human's whereabouts, they said they thought they may have seen one near the center of the town by the small building that was currently being renovated to become a restaurant. He didn't catch the name fully, Grill something, he was too preoccupied to care. With his black coat trailing behind him, he clutched his white turtleneck closer to his face and pressed forward through the depressingly snowy landscape. As he began to look around, the white orbs in his eyes scanning all there was to see, he suddenly caught a slight movement behind a group of pine trees. Narrowing his eyes he moved forward towards the movement until he was right up to the trees. He reached out to part them, but suddenly stopped himself. What if the human was scared? He didn't want to frighten it away, that would just take more effort to find them again, and he certainly didn't want to waste any more time in this dreadful place.  


Instead he softly called out "Human? Is that you?".  


A small gasp was audibly heard, and the tree seemed to rustle in shock.  


"Please, I am... I am here to help you. I want to help you." Gaster spoke softly once again, making sure his voice was as calm as he could possibly manage.  


After a few moments a wavering voice spoke out quietly ,"Are you going to hurt me?"  


The sound of the voice made his heart pound in his chest, as he knew no monster would fear him, nor hide from him. "No," he called out, "I will not. But you have to come out, there may be others here that might, and I want you to be safe... and warm."  


The last part is what ultimately what Gaster had hoped would entice the human to come out, warmth, as he imagined they had to be chilled to the core. He stepped back as the trees began to rustle again, and he brought his hand up to his mouth to bite his bony knuckle as he saw what came out. It was indeed a human, but it was such taller than he had expected, as he had only seen them depicted in drawings from historical documents dated well before he was a scientist, or even around for that matter. The human was wearing a blue fur-lined hooded coat, red scarf, and long pants, but the clothing looked like it was doing little to block out the chill of the air. The human's skin also seemed to be of a pale bluish hue, and their lips trembled at the cold, as well as the towering sight of him.  


"Will you really h-help me?" the Human asked bashfully as they averted their eyes to the ground to avoid Gaster's stare. The sight of his lanky imposing form and slightly cracked skull at the top of his right eyesocket was enough to send anyone running for the hills, but they were too exhausted to even barely move, let alone run.  


"Yes, if you come with me, I will take you to a safer place than this." He replied, holding out his long slender arms.  
With a deep breath the human stepped forward, but their numb legs decided not to function properly, causing them to fall into Gaster's outstretched arms. Gasping sharply he jerked forward to catch the human quickly, as he didn't want any harm to come to them before he could at least talk with them.  


Slowly realizing they were in the arms of a creature, an extremely tall skeleton creature none the less, the human tried to speak out, but the shock of the moment was all too much and they fainted in his arms.  


"Note to self," Gaster spoke quietly, almost irritated at the situation at hand, "Humans are incredibly frail and do not handle the cold well. I'm going to have to carry this one after all, and it's such a distance to my lab." He closed his eyes with a sigh and suddenly three pairs of skeletal hands appeared around his darkened form. When he opened his eyes, one eye burned blue, the other burned orange, and all six of the conjured hands grabbed the human's limbs in different places to carry them off to the boatman that was waiting in toe on the bank of the river. It was a great deal of effort to use his magic this way, but he knew it would be worth it in the end.

_____________________________________________ 

The human remained in an unresponsive state for days, and for each day that they remained unmoving Gaster began to fall into a state of despair. He questioned if the human would ever come around, but he had hope as long as he could still see their soul glowing faintly pink in their covered chest. Finally one day while writing some unrelated research down, he heard a faint sound come from the bed that the human was placed upon. Throwing his chair to the side, he swiftly rushed over to the bed and looked down over the human to see if they were waking up. The human fluttered their eyes open, and as soon as everything around them came into focus, including the lanky skeleton before them dressed in black, they jerked up and let out a scream. Gaster was so startled by the human's reaction that he stumbled backwards and began to wave his hands at the human.  


"No, please, none of that!! I'm not going to hurt you! I helped you!" He pleaded as one eye began to faintly glow blue in his eye socket.  


"Wh-where am I?!" the human snapped after they stopped their scream.  


"You are in my laboratory. You fainted from exhaustion when you came out from the trees and I bought you here to get well." Gaster explained as he lowered his hands and closed his eyes to calm down. With a deep breath he opened his eyes back open again and looked down to the human with an attempted comforting sort of smile. "My name is W.D. Gaster, and I am the Royal Scientist here in the Underground. I mostly work on projects for the King of this land, but I must admit I am quite fascinated about humans and human history. I guess you could call it a hobby of mine..." He laughed softly, a strange ethereal sound emitting from his throat that made the human appear uneasy. Clearing his throat, Gaster walked over to the chair that he was sitting at, picked it up off the floor, and wheeled it over beside the human, taking a seat.  


"How... long was I asleep?" the human questioned.  


"About five days, give or take, I so often lose track of time down here."  


Gaster slowly moved his hand to the human's as he gently placed his fingers on their wrist to check their pulse. The human jerked slightly to his touch, but quickly realized that he was only trying to check their vitals.  


"Do you remember anything about how you got down here? Perhaps how long you were in Snowdin?" Gaster asked as he removed his hand from the human's wrist and placed the both of them on his crossed legs.  


The human bit their lip and looked around the dimly lit laboratory. "I, um... I don't know exactly. I was going for a walk after I had a fight with my boyf-... after I had a fight. Suddenly I tripped over something, and I just kept falling down into the darkness. I woke up in a dark cave filled with all these flowers, it was odd, as if they cushioned my fall. My head hurt though when I woke up, I think I may have hit it. I decided I was fine enough to try to get out of the cave, so began to walk... I went through these, ruins? Then exited out into the snow. I didn't have any other choice, and I thought maybe that it had snowed over night when I was in the cave, but then I saw these... creatures... walking around, and I was terrified." The human looked down and blushed at the mention of the word terrified. She felt mildly ashamed that she would use such a term, especially in front of one that saved her life. "I ended up sneaking into that small town, and I tried to stay hidden as best as I could, but the creatures there -"  


"Monsters," Gaster corrected, "we are monsters."  


"Oh, I'm sorry, um monsters there kept trying to find me. I was running out of options and warm places I could hide, but then you found me..."  


"And not a moment too soon, I fear any longer and you would have frozen to death! It would not have been very conductive to my research."  


The human looked up and into Gaster's eyes, a look of fear playing across their face. "R-research?"  


Gaster laughed again, the same ethereal sound escaping like once before, but this time he smiled brightly at the human. "Yes, research! But don't worry, I will not harm you in any way, I already promised you that when we first met. No no, I want you to tell me all about you humans, and your lives. I want to learn everything I possibly can about them so I can further my research. You see, I am studying this thing that has been called "Determination", something humans possess a great deal more of than monsters do. From the looks of it, and how you survived not only the fall down here, but the extreme cold, you are full of "Determination", and I want to know why."  


The human looked over Gaster slowly as he began to talk so excitedly about his current, but limited, research. They noticed that as he opened up he seemed to talk with his hands quite a bit, more so than they had ever seen another person talk. His gestures were so fluid, so mesmerizing, not quite sign language, but something similar. Eventually they came to notice that in each hand were large holes, big enough to see through.  


When Gaster was finished, the human looked at his eyes once again and asked quite unabashedly "Your hands, do they hurt?"  


Shaking his head slowly, Gaster clasped his hand to the other, tracing his finger tenderly around the rim of the hole. "Not... anymore. The pain faded away... after time."  


Realizing that their question was incredibly rude and blunt, the human apologized, and looked away. They were just so curious by the look his hands that they couldn't help but ask.  


Then Gaster retorted swiftly, a slightly irritated tone raising in his voice"If we are going to ask each other blunt to-the-point questions, then I must know, are you a boy or a girl? I need to know if we are to begin my research."  


"Fair enough," the human said. "I am a girl, a woman to be exact, definitely not a child as the term girl might imply. You can call me-"  


But Gaster didn't hear her name, he was once again too preoccupied with his inner joy that he would finally have a human, a female human, in his laboratory to talk with and hopefully one day conduct further research on. This human was all his, and he would finally get the missing pieces he needed to complete his work.


	2. Commence Research

**Summary for the Chapter:**

> Gaster and the human begin to get to know each other better.

**Notes for the Chapter:**

> *** Update 7/9/16 - I decided to break up the original story, now known as "Chapter 1" into two separate chapters to make them more inviting to read (I prefer shorter chapters). This is the second half of the original short one-shot (which has become a chapter story). ***

Weeks passed as Gaster and the human got to know each other. He did everything he possibly could to keep her happy; he had comfortable clothes made for her, had his "Followers" prepare food for her, and attempted to accommodate her every need. Occasionally they would go for walks around the Hotlands, a place that she liked considerably more than Snowdin, especially now that she didn't have to wear her bulky blue fur-lined coat everywhere, as well as a place that Gaster said was the beginning stages of the "Core", which he had recently started to build under the King's direction to supply electricity to much of the Underground. They talked about anything and everything related to humans, and she told Gaster all she could about human emotions and actions. In such a short time Gaster had learned so much knowledge from the human, but one thing still remained on his mind as they often took their strolls, and that was how the human body functioned and felt. Granted he had asked her several times, and she told him as much as she knew from the basic lessons she had learned at school and something called "colleg", but despite hearing about the inner and outer workings of the human body, he wanted so desperately to see what it looked like underneath the clothing she wore, and feel how her flesh, bones, and muscles felt to his bony hands.  


One day during an especially interesting conversation with the human at lunch, Gaster decided to ask the human how she felt about furthering his research on the human anatomy. 

"I have been meaning to ask you, and please know that I hold you in the highest respect when I say this, but I have been ... curious ... about studying the anatomy of humans closer, as you may have suspected at all my questions as of late. Everything I have seen thus far are of drawings, and not the best drawings at that. Only occasionally have I been able to find medical charts in the Dump, but they are so often missing pieces of vital information. You have told me that human bodies are filled with nerves and the flesh is so sensitive, I was wondering if I could perhaps do some investigating on your body. It would be solely for research, I assure you."  


The human knew she owed her life to Gaster, and after the last few weeks spending time with him, she had begun to develop a deep respect and fondness for the scientist. The thought of exposing herself to him was a bit frightening, but she knew he would never cause her any harm, so she agreed to his proposition.  


"Splendid!" He exclaimed throwing his hands up, knocking over his water glass in excitement. The human giggled as he bent down to pick up the shards of glass that littered the ground. "Oh, I am sorry, but you have no idea how happy this makes me! Tonight, can we do this tonight? I... I feel like I have been waiting so long already."  


"Yes, tonight." The human nodded and swallowed slowly, deciding that she suddenly did not feel like finishing the last of her lunch. "If you don't mind, Gaster, I'd like a few things to prepare myself for tonight. Could you get them for me?"  


"Anything you want!" Gaster said breathlessly as he attempted to control his excitement.  


"Thank you, I'll give the list to one of your 'Followers' when I return to my room. I will see you tonight then." And with that the human excused herself from the table, and made her way back into the laboratory, clutching her arms as a great feeling of nervousness began to set in. She knew she would probably look horrible in her current state to any man on the surface that may have wanted to be see her so exposed, so she wrote some personal item requests on a piece of paper, handed it to one of the the gray "Followers" that always seemed to be around when she or Gaster needed them, and sat down on her bed with her face cupped in her hands, wondering how she could have agreed to what was about to be done to her.

\------------------ 

She had bathed herself thoroughly and cleaned up as best as she could given the nature of the objects she had to do so with. Placed on her bed at some point while she was in the bathroom was a soft black robe that one of Gaster's "Followers" must have laid out for her. Slowly putting on the robe, and nothing else, she looked at her body in the mirror before she closed the robe and walked out the door of her room. It would have to do, she thought darkly to herself. The walk through the hallways seemed to take forever even though Gaster's examination room was only a few doors down, and each step she took closed filled her with a slight sense of dread. She finally approached Gaster's door and knocked gently, quietly, almost weak enough that she had hoped he wouldn't hear her, but alas, so such luck. The door flung open as if he was standing on the other side waiting, and Gaster stood in the doorway with a wide grin and his eyes burning bright white in the dark sockets of his eyes.  


"Come in, come in! Please, make yourself comfortable, at home!" He burst out, then quickly attempted to control his excitement, holding his hands down upon his lap. "Ahem, I'm sorry, excuse me. Please, have a seat on the table, do you need anything before we begin?"  


The human shook her head no and proceed to the table, clutching her robe to her chest. Her heart was beating so fast, and she could not fully explain why, as all he wanted to do was document how her body looked and felt. As she sat down Gaster made his way to the side of her, taking a brief seat in a chair to discuss with her about was about to happen.  


"I would like to begin with your back side if you don't mind, I am most fascinated at your spine and how it feels in relation to your body since it basically connects the entire human form together. Before we proceed, I must show you how I will document your body. Please do not be alarmed..." Gaster stood up from the chair, moved directly in front of her, and closed his eyes. An oddly static-y sound began to fill the air around them, and as Gaster opened his eyes back up, the human noticed one now burned bright orange and the other burned bright blue. Shifting her stare away from his eyes she suddenly noticed that Gaster's body was surrounded by six floating skeletal hands, each of which had holes in the center just like his actual hands. "I am going to use my powers, my hands, to explore and document your body, as I think it would take forever if I did it with just my own two hands. Also, to help the process, I will be speaking in a language that you might find odd, but just know that this will be so only I can access my research on you for the time being. We may begin anytime you are ready, unless you have any questions?"  


The human had LOTS of questions, but she decided that now was probably not the best time to ask since she just wanted to get this over with.  


"No, I think I am good for now..." She weakly stated as she stood up. Closing her own eyes, she released her grip on the black robe and let it fall to the ground in front of her. As she did so she audibly heard Gaster gasp out, as well as the unmistakable sound of him biting his knuckle, something he did quite often when a subject intrigued him the most. "Fascinating, so completely fascinating" she heard him say, and instantly a flood of heat rushed to her face as she turned around to hide her embarrassment. He could feel Gaster's stare burning right into her soul, but she decided to ignore that for now, and climbed up onto the table, laying on her stomach first as instructed. It was at that moment that one of Gaster's conjured hands first touched her back, making her gasp in shock. Gaster apologized for surprising her, but she could barely hear it as her ears begun to burn and tingle with embarrassment as all six of the hands began to set upon her, gently tracing their digits across her flesh. They seemed to almost crawl up and down her spine, working their way along her neck up to the various contours of her skull, then back down around each rib with such curiosity. The feeling of all the hands upon her slightly shaking body was both invasive and welcoming as sometimes they would poke her, but then softly rub as if she was getting a massage. As the embarrassment began to die down in her face, and the shaking in her body eased up a little bit she could hear Gaster speaking in a strange ethereal language, something that was similar sounding to the way he would laugh. She would occasionally glance over to him as he walked back and forth, staring at her body with such amazement, waving his own hands around as if conducting an orchestra. His stares did little to calm her nerves however, something about the ways his eyes lit up with such joy at looking at her was more powerful and exciting than any man had ever looked at her on the surface, and she began to feel her insides stir with a sickening sort of arousal, something she knew was absolutely not ok in any sense of the word.  


Sometimes as Gaster began to explore further the hands would accidentally tickle her in places that she was not use to being touched, and she would giggle out, quickly scrambling to regain her composure. Gaster always noted each outburst in his ethereal language, minor or not, and made sure to document each sensitive area of her back side. She almost felt as he found some sort of pleasure at the tickling, but there was no reason to currently ask as she didn't want him to stop and interrupt the feelings she was experiencing. She figured she would ask him later on.  


After about thirty minutes or so, the hands gently lifted off her body and Gaster spoke in his normal voice, save for a slight tinge of the ethereal sound that still lingered in the air. "Would you please flip over so I can document the other side?"  


In an instant the heated flood of embarrassment washed over the human again as she slowly shifted her position to expose the front of her body to Gaster. She did her best to keep her legs clasped firmly together as she did so, as she knew she had already begun to grow wet from excitement, but she tried to play it off as if she had a bit of a cramp from laying on the table for so long.  


"Relax please, and spread your legs a bit if you would. I need to be able to feel everything, and it may be a bit difficult to do so if you aren't relaxed." Gaster said in a slightly demanding tone.  


Yeah sure, 'relax', she thought. Easy to say but not easy to do given the tension of the situation. She swallowed hard as the hands moved in upon her once more and began their continued exploration. They started off with the top of her body, cupping her face and skull tenderly, running their fingers down her neck, across her collar bones, and then down her sternum onto her ribs. As some of the hands approached her breasts, she sharply inhaled as they traced their fingers along the sensitive parts of her flesh and winced slightly as they gently rolled the points of her hardening nipples in their digits. She looked over to Gaster as the hands did so, as if to plead him to stop, but she could see that he was almost in a trance of speaking and conducting his hands, his eyes wildly burning with satisfaction. He couldn't possibly have had any idea what he was doing to her, yet once again she almost felt as if he knew what that was doing to her, and he was doing it on purpose so he could see what reaction it would cause. Rolling her head back over she bit her lip and waited for them to finish before moving on to other parts of her body. The lower the hands went though, the more and more nervous she became, as she knew what might happen if they touched a certain part of her body. Why hadn't she set boundaries before they started? Why didn't she tell him that some areas on her body were more sensitive than others? They had never discussed human sexuality before as she never felt the need, but now she was wishing that they had so he could understand what he was doing her her.  


The hands kneaded down her stomach, landed upon the tops of her hips, and she bit her lip harder as they began to move lower and lower. However, the hands on both sides decided to slide down the outer sides of her thighs and legs instead, and slowly made their way down to her feet to explore. A sigh of relief escaped her lungs as they started to trace across the bones and pads of her feet, and she thought for a moment that Gaster would be finished shortly. However, a rush of panic instantly began to fill her again as they started to make their way up her inner legs, then her thighs. Her heart began to pound in her chest harder than she had felt in a long time, and the feeling of the hands creeping up her inner thighs caused her to begin to break out in a sweat. Suddenly one of the hands brushed gently across the exposed and incredibly sensitive lips of her mound, and before she could stop herself, she moaned out loud and arched her back against the table.  


At the sound of the human's moan, Gaster quickly jerked his hands away from her exposed body and rushed over to her side, the conjured hands dissipating into the air. The magic in his eyes quickly faded away, and he bent down over her to make sure she was ok.  


"I'm so sorry, did I hurt you? Are you ok? What was that?" He slammed her with questions, but quickly noticed that her face was flushed red, and her eyes were averting his. "...I ... I didn't hurt you, did I."  


"N...no" the human managed to squeak out.  


Gaster stared at her with a puzzled look on his face. "If it didn't hurt... did it... feel good? I'm incredibly confused."  


Hesitating for a moment, the human then nodded slowly, swallowing hard and biting her lip once again.  


"May I explore once again in that area? I'll do it with my own hands this time, and I'll be more gentle" He asked, moving down slightly on the bed so he could be closer to her legs.  


"........Yes." She answered quietly, her heart beating even faster.  


Gaster moved his hand down her to her mound and gently traced his bony fingers along the line of her closed lips. He could hear her gasp again, and the sound intrigued him enough to spread the lips open slightly with his index and ring fingers. The human moaned again and turned her head away from him, but did not tell him to stop, so he spread her lips open a little wider to see what the inside looked like. As he looked at the sensitive area, he could see it glisten with a sort of wetness, and as he moved his head in closer he could smell an intoxicating sort of scent that he had never experienced before. Upon further investigation he saw a small pink button like object, and out of sheer curiosity he decided to brush his finger along the side of it and trace it down near the opening that appeared to be where the fluid was coming from, his finger gathering quite a bit of the interesting wetness in the process. In an instant the human moaned deeply, and he jerked his head back up to see if she was ok. Her eyes were closed, but she had begun to pant heavily, and Gaster didn't quite know what to do. Her composition had changed so quickly, in mere moments she went from being perfectly fine, to being out of breath without any physical effort on her part. He stepped back baffled, turned, and slowly looked down at his hand that had been exploring her sensitive area. Bringing the hand up to his face, Gaster examined the liquid a bit closer, smelling it in the process. It was even more intoxicating up close, and out of sheer curiosity he placed the wet finger into his mouth so he could investigate if there was any taste to go along with the incredible scent. Indeed there was, and as he rolled his tongue around his finger he closed his eyes with a slight swoon as the flavor of the human griped his senses.  


"...Do you like it?" The human quietly asked, her breasts rising up and down between deep breaths.  


Gaster blinked and pulled his finger out of his mouth, turning back to face the human with a faint purple looking sort of blush spreading across his face. "I..."  


"Do you... want to taste more?" She questioned.  


"...Yes." Gaster replied, the blush spreading further, the whites of his eyes fading out replacing his sockets with complete darkness.  


The human nodded to Gaster and gently moved down to the edge of the table, spreading her legs wide enough so he could get in. "It's....it's ok, I... I want you to as well."  


Harshly biting his knuckle in anticipation, he moved between her legs, knelt down, and began to trace his fingers along her inner thighs, trailing forward slowly to her glistening exposed mound. With eyes closed tightly shut he inhaled her scent once more, and when he opened his eyes again they burned a new shade of color, neon purple. As he moved only inches away from her mound out rolled a neon purple tongue that seemed to glow with magic, much like his hands did when he conjured them. His first lick was gentle, but regardless of pressure the human on the table before him squealed out in pleasure, her hands gripping the table tightly. The taste, he had to have more, so he began to slide his tongue up and down her insides, swirling and exploring around every wall and crevice. He noticed that the human began to moan out the most when he licked at the enlarged pink button near the top, as well as found out that with further stimulation more of the delicious fluid would leave the flexing hole near the bottom. With an almost animal like instinct filling him up, Gaster growled softly as he traced his tongue down to the opening, sliding his magical tongue inside the hole slightly, looking past the human's legs onto her face to see her reaction.  


The human gasped out and moaned again, looking directly into Gaster's glowing neon purple eyes. The sight of his eyes wildly excited her, and she could feel her insides burn hotter with stimulation as he continued to slide his tongue in and out of her opening, as well as lap up and down her pussy.  


"Gaster, I'm going to... Just d-don't stop!" she panted as she watched his face bury itself into her dripping mound, lapping up her juices as if he hadn't had a drink for years. Suddenly the feeling was all too overwhelming as he growled against her once more, and her body began to react as an intensely powerful orgasm washed over her body, making her shake violently, her toes curling in the process. With the loudest moan thus far escaping her lips her opening released itself, and out came a rush of the sweet liquid that Gaster had been trying so desperately to consume, coating the tabletop below her, dripping down onto the floor.  


Gaster looked up at the human after her juices had stopped flowing with amazement in his still glowing eyes, and he raised himself off the floor, standing silently at the edge of the table, looking over her body. He noticed that her eyes were fixated on something else, something on his body, and when he lowered his gaze to meet the object that she was staring at, he gasped in shock. The front of his pants was bulging out against the fabric and glowing faintly of neon purple. He blinked in disbelief and traced his hand across the bulge, inhaling sharply at the pleasurable sensation of it.  


"Show me." The human said as she propped herself up on the table, letting her legs hang over the edge on either side of Gaster.  


"I don't know... what is happening to me. I don't know, what this is?" He exclaimed as he looked up at her with an incredibly concerned look on his face. " I-I feel like my body is burning, but not in a bad way."  


The human reached her arms forward and gently brushed one of her fingertips against the bulge, causing Gaster to sharply inhale again. She then moved her hands to his belt buckle, unhinged the latch, and carefully zipped down his pants. Gaster brought his knuckle up to his mouth again, biting hard this time, as the human pulled out the glowing purple object that had manifested itself inside his pants. He had no idea what it was, or how he or his mind had known to manifest it, but it seemed to throb with intense magical energy. As the human ran her fingers down the length of it, he began to pant just as she had done.  


"Do you know what this is for?" The human asked, tracing her soft fingers around the tip of his erection. She was absolutely intrigued in regards to how a skeleton monster could even conjure up such a thing, but she wasn't about to object, especially given the look of embarrassment that overshadowed Gaster's normally happy looking face.  


"No, can you tell me? I am, uhhhnnn, absolutely baffled."  


The human smiled coyly at his moan and bit her lip, absolutely shocked and mortified at what she was about to say.  


"You put that inside me."  


Gaster gasped at the thought of what she had just said, and had half a mind to stop the research then and there, as it had clearly gone beyond the point that he had thought it would go, but a burning curiosity and desire filled his body at the thought of being "inside" the human, so he took his glowing member into his hand, and moved forward against the human's body. The feel of her body against his throbbing magical piece made his eyes burn brighter in his skull. He slowly traced the tip of it down her soft wet flesh until it set against her hole that seemed to begin to widen in anticipation of his entry. He looked to her for a sign of some sort, and after she nodded to him, he gently pushed his hips forward and slid the length of his member inside. The two of them moaned in unison as he pushed it all the way in, pausing for a moment to collect his thoughts and whisper his findings in his ethereal language.  


As the human clutched at his coat as he began to slowly pump in and out. Quickly, as if he had known what to do all along, he found a rhythm and began to pick up the pace. Between his groans he began to speak in both his normal language, peppering in spots of his ethereal language, but none of it made sense to the human below him. Suddenly he began to growl, and his hands grabbed at her hips tightly to gain more leverage as he began to buck into her even harder.  


The human screamed out in pleasure, tossing her head back as he began to hit a very tender spot deep inside her, and she began to feel her insides burn with the once again familiar feeling of an oncoming orgasm.  


He could feel something inside him happening too, an unexplainable pressure building up inside his body, and he tried to not fight it despite the alarming nature of the situation. Suddenly, he felt the insides of the human clench around his throbbing length, squeezing it tightly as he continued to pump in and out. The human began to shake once again, and with some sort of new found energy, he thrust upon her as hard as he could as she convulsed around him, gasping for air in between screams. All at once Gaster felt an incredible urge shoot through his body, an urge to release, but he began to panic at the unfamiliar feeling. Quickly reacting to the foreign feeling exploding inside his body he pulled his spasming member out just in time for ribbons of glowing purple liquid to shoot out, coating in the human's mound and stomach thoroughly. He shook violently and groaned as the baffling new fluid escaped his body, and after he had finished completely, his skeletal form collapsed down onto the floor, trying desperately to catch his breath.  


With the soft sound of fleshy feet hitting the ground, the human rushed over to Gaster's side, knelt down, and placed her hand over his, the other cupping his face to lift it up to hers. The glowing purple in his eyes had dissipated, and was once again replaced with the familiar glowing white orbs.  


"Are you ok?" The human questioned, a strong concerned tone ringing out in her voice.  


Gaster nodded and sat up, looking down to see that his magical member had completely disappeared, along with any traces of the purple liquid that shot out from it. For once he couldn't think of anything to say, but he didn't need to as the human moved forward onto him, wrapping her arms around his chest, burying her face deep into the fabric of his turtleneck. He wrapped his arms around her in return, clutching her tightly to his still slightly heaving rib cage.  


After holding each other for quite some time, Gaster whispered gently to the human, now half asleep in his arms.  


"What we did, we did for research, right?"  


"Yes, for research." She sighed softly as her body began to get heavier in his arms.  


Gaster closed his eyes and smiled, feeling the human slowly fall asleep in his arms. He never expected anything like this to happen to him, nor did he know he was capable of such magic. He sighed in content, ultimately happy with how his research had gone, completely unaware that between his left eye socket and mouth, a new hairline fracture had begun to grow...


	3. Discovery

**Summary for the Chapter:**

> Gaster had been missing for several days following the "research" that had taken place between the him and the human, and in her loneliness she decided to break the rules of the laboratory and seek him out. What she discovered though, she should have left alone.
> 
> Follow my Tumblr at http://esperaqua.tumblr.com/, it's where I post my Undertale Cosplay photos (both SFW and NSFW), and chapter updates!

"Gaster....I, I, aaaahhnnnnn!...." The human jerked awake from her dream, dripping in sweat, clutching her hand out into the darkness of the empty room. Her moans still rung out in her head as she tried to fumble around for a lamp of some sort, but her fingertips found one to no avail. As she sat alert in the darkness, sweat trickled down her forehead as she recalled the "research session" from the other night. She still couldn't believe that the two of them had done such a thing, and it made her nervous just thinking about it. However since that night he seemed to have been avoiding her like the plague, as she hadn't seen him for days, and it made her heart ache thinking that she may have done something terribly wrong by allowing the two of them to take it so far. 

As her eyes adjusted to her surroundings she tossed the covers aside and placed her feet on the cold tile flooring, shivering slightly as she made her way to the door, deciding it was time to confront him about their transgressions. She simply had to know how he felt about the situation, and wanted to talk with him on any subjects he needed explained.

As she entered the hallway, she noticed not a single monster was out and about, which was incredibly odd because one of Gaster's several followers was almost always near her door in some capacity, ready to help her out with anything she needed. 

"Hello?" She called out into the quiet surroundings, only her voice echoing back at her. As her unease grew more prevalent, she began to peek inside some of the rooms, something she had never dared to do since she became a guest at Gaster's Laboratory, as it had been his number one request when she first began to know him. To her dismay she found them empty as well, completely void of all light and life. What time was it? Where was everyone? Why was it so damn quiet?!

As she turned a corner into a hallway she normally stayed clear of, she saw a faint blue glow underneath one of the doors. Pausing for a moment, she looked to the doorway with curiosity. Her insides screamed to stay away, but the light beckoned her like a moth to the flame and she could not help herself from moving forward. Pressing her ear up to the door, she listened first before just barging in. She could hear the faint sound of what seemed like water gently bubbling, as well as the electronic hum of machinery. It seemed peaceful, serene almost, and it made her want to investigate further, even though she knew it probably wasn't one of the best of ideas.

Placing her hand on the handle she pushed forward and entered the room. In front of her was the typical lab setup she had seen in Gaster's other rooms, beakers of colorful liquids, Bunsen burners, various tools, but in the back of the large room were dozens of metallic tubes coming out of the ceiling connecting to two large glass cylinders, roughly five or six feet in size. The blue glow and soft bubbling sound that had initially drawn her into the room were coming from the large cylinders, but unfortunately the contents inside were not directly visible at a distance as two sheets were haphazardly draped over the front of each cylinder. Her legs seemed to move on their own as she slowly made her way toward the light, but a little voice in her mind began to scream 'No, turn back, you don't want to see what may be under those sheets! It isn't our business, it isn't our right, stop!!' Before she even realized it, she stood in front of the glass, her heart nearly pounding out of her chest. 

A bead of sweat trickled down her temple as she raised her hand and touched the sheet softly, taking care to not distress the fabric too much, as she didn't want to leave any evidence that she was even in the room. With a deep breath she pulled back the fabric slightly and moved her face to the glass surface to peek inside. Nothing, there was nothing. No wait, there was something small, but as she twisted her face to make out what it was, nothing immediately came to mind. The best her brain could process what she was seeing was a sort of small white... Oh god. She dropped the fabric and took a step back, covering her hand to her mouth to stifle a gasp. 

"Is that... a skeletal fetus?" She whispered as she blinked a few times to process her thoughts. Her eyes instantly moved to the glass cylinder on her left, and her curiosity got the better of her once again. However this time her heart was racing so fast that she didn't take the care she had done previously, and her hand accidentally gripped the fabric too strongly, causing the entire sheet to slide down, exposing the contents inside. A slightly panicked yelp escaped from the human's lips as she saw what was inside--- a toddler sized skeleton, curled up in a fetal position. As if sensing something was in the room with it, the small skeleton behind the glass suddenly opened one of its boney lids and looked directly at the human in front of it, white pinprick lights just like... Its eyes remained on her for only a few seconds before they moved up to look at something beyond her.

"You. You shouldn't be in here." A deep and angry voice sounded off from the doorway, a voice she had never heard before, yet had. Her heart nearly stopped as she suddenly felt a hand grip deep into her hair, yanking her away from the glass cylinder before her. Out of the corner of her eyes she saw the sheet rise up off the floor by a disembodied hand, and at that moment she knew who was in the room with her. 

As she struggled against the force pulling her backwards by her hair, she was quickly spun around by a set of hands, which swiftly moved down to her own hands pinning them together behind her back in a cuff like fashion, effectively binding her limbs to her body. Her eyes widened as Gaster stood in front of her, towering over her, his black frame practically sucking all the light out of the room, especially now that her back was turned to the glow. His face had changed since the last time they were together, a new crack had set into his skull just below his left eye socket, running nearly all the way to his mouth, and the one above his right eye socket had grown much longer. 

"Gaster, I- I'm so sorry! Please let me go!" the human pleaded as she continued to struggle against his conjured bindings. She wasn't necessarily in any real pain, but her heart felt like it was about to explode out of her chest.

As Gaster looked down upon her, he narrowed his eye sockets, his mouth forming a scowl. "I've asked you before to not explore on your own, and this is where I find you? Of all places, this room?!" Another hand conjured in the air and set upon her throat, cupping it firmly, applying pressure but allowing her to breathe. "Do you have any idea what could have happened if you would have touched something you shouldn't have? Do you have any idea how delicate and special this research is to me?!" As Gaster's voice grew more and more upset, the hands began to increase their grip on the human's hair and flesh. He could see her wince, but his anger blinded him beyond caring at this particular moment in time.

"Ahhhn, please, I didn't know!" A distressed moan escaped her tightening throat as the hand in her hair pulled her back a bit more, forcing her to look directly in his into his eyes which wildly blazed orange and blue. "Th-there was no one around, everyone was gone, I only wanted to find you! To talk to you!" A single tear rolled down her cheek as she bit her lip, "I... I missed you..."

Gaster's left eye twitched as the hands eased up a bit, but he still kept her firmly in place. "Missed me?" His hissed and drew his body back some, then paused and thought about her words for a moment. "I'm going to let you go, but I want you to go to your room immediately. If you hesitate, I will use force, do you understand? Get out of here now, we will discuss... things... momentarily."

"Yes! I will!" The human choked out her words as the hands released themselves. She quickly scrambled to get her bearings and ran out of the room, the door slamming loudly shut behind her as she ran down the corridors. As soon as she reached her room, she quickly shut the door behind her, collapsing onto the cold tile, heavy sobs escaping from her chest. 'Why was I so damn curious?! Why did I have to go in that room?!' she thought to herself as she wiped her tears off her burning cheeks. She always knew curiosity killed the cat, and this time she only made it out by the wisps of her whiskers. She knew Gaster was strong, and his magic was quite powerful, but this was the first time she had seen him so furious, and she was thankful that in his fury he didn't just snap her in half like a twig. 

As she began to calm herself down, a sudden realization came into her mind, her panties were damp, and her clit was throbbing with excitement. The experience had scared her so badly, but the thought of Gaster's forceful nature sent shivers down her spine. The way she felt so helpless as he towered over her, pinning her back, his hand clasped over her throat, it was horrifying yet so completely exhilarating. Swallowing hard at her unease she collected herself off the floor, made her way over to her bed, and sat there alone in the dark waiting for Gaster to come "discuss things momentarily." She hoped and prayed he would be a bit more calm when he came to talk with her, but also secretly wished he would show her that power again. Fuck, what did she get herself into?  


\----------------------------------------------------------------------------

Gaster's hands clenched together tightly as he made his way over to the cylinders, making sure to check over everything carefully. To say he was upset was an understatement as he just couldn't believe the human would disobey such a simple request, especially given all the other freedoms and luxuries he had given her. After he finished checking the valves and vitals to make sure everything was ok, he walked over to a table, growled deeply, and slammed his fists down onto the surface, causing several of the jars to rattle loudly in place. Closing his eyes, he sighed loudly then looked back over to the covered cylinders, his precious experiments...

"I... I can't let this be acceptable. I can't let the human think that she can just walk all around this laboratory unsupervised." Gaster's hand moved up to his skull and traced a bony finger long the crack just below his eye. "I've sacrificed so much, worked so hard, I can't have some foolish human come in here and waste it all. There are just too many things that she could damage. Or discover. Or destroy."

Inside he felt so conflicted about the situation. One half of him wanted to go into the human's room and punish her for refusing to follow his direct request, but the other half was just too enamored with her to even want to harm a hair on her head. As his mind buzzed with a barrage of emotional conflicts, he leaned against a wall and sunk down to the ground, his hands moving up to his skull, holding his face in the palms of his holey hands.

"She said she missed me," he whispered as he closed his eyes, "She was just trying to find me..." It was true, he had been gone for a few days, but it was of no fault of his own, as he had been called away for business by the king almost immediately after they had... had... His face flushed a light purple as he recalled the events of the other night, the way her flesh felt underneath his hands, the way her unique fluid tasted against his tongue, the way her body squeezed and contorted around his glowing member. 

Gaster opened his eyes slowly to see the newly discovered faint purple glow emanating from his pants once again, and he moved a hand off his skull to trace along the growing bulge that grew on the other side of the fabric. Honestly, while he was working on the Core over the last few days, he had little time to think about anything else, let alone the events that transpired a few nights ago, but now that we was left alone with his thoughts, he began to grow restless and hungry. His eyes fluttered over to the door where the human had been as he grasped at the stretched fabric tightly, stroking back and forth a few times, a worded moan escaping from his throat. "Human..." Pulling himself off the floor he adjusted his pants, smoothed out his coat, and attempted once again to collect his mind. His anger had all but subsided, but was now replaced with something more intense, a deeply seeded animalistic lust. He knew at that moment how he was going to teach her a lesson, and he quickly made his way to her room to do so.


	4. Punishment

**Summary for the Chapter:**

> The human learns the lessons of disobeying Gaster's requests....

Gaster made his way down the winding hallways swiftly, dismissing his Followers for the night whenever they tried to warrant his attention. They looked confused as they were brushed aside, Gaster's coat practically waving them away as he passed them by. As he approached the human's doorway, the last Follower in the area looked up at him with a surprised look on their face.

"Leave, I have something I need to discuss with the human, and I don't want to be bothered during my discussion. Is that clear?" Gaster growled out at the small Follower. It nodded and quickly scrambled off, not wanting to find out why his Master's tone was so harsh this evening.

Gaster raised his fist and motioned to pound on her door, but stopped just millimeters away from the metal. 'Why give her the satisfaction of _allowing_ me to enter a room in my own lab?!' he thought sharply to himself, 'If she can't respect me, I won't respect her'. With that he decided to just enter the room without asking, returning the "favor" to the human, as all bets were off at this point. Opening the door as forcefully as he could, his glowing white eyes instantly locked onto her body. He noticed she was sitting on the edge of the bed in the dark, her hands clutching the sheets in shock at his intrusive entrance.

"Gaster!!" The human yelped, her heart leaping into her throat. She stood up quickly, her hands clutching onto her arms, attempting to hold her own body in a protective way. She began to shake at the sight of him in the door frame, he was so completely fixated on her, but his eyes said nothing of how he was currently feeling. Swallowing hard, she squeaked out "G-gaster, I -"

"Quiet. Don't talk. Don't move. I want you to listen to me." Stepping forward into the dark room, he closed the door behind him, encapsulating them both in complete darkness. Despite the pitch black of the room, Gaster could still see the human, who looked around the room confusingly, biting her lip, trying so desperately to see where Gaster had gone. He walked to her side, leaned down to her ear, and slid his bony hand to her chin, tilting her head back as he began to growl harshly.

"You. You completely disobeyed me. How exactly should I take that? What exactly should I do with a human that won't listen?" He smirked as he heard the human whimper at his words, completely pleased at her reaction. "I could lock you up. I could make you sit in the darkness until I needed you. I could do terrible, awful things to you. I could... tear you apart and dissect you, if I really wanted to." He snapped his hand off her chin and moved to the backside side of her quickly, conjuring up a pair of hands to grab her hands off her arms. He brought them up above her body, holding them in place, a surprised moan escaping from her lips. He moved a little closer, tracing his finger down her spine, making her whimper out again.

"I don't want to do those things though, you are too valuable to me, too precious." His voice changed its tone slightly, a soft ethereal tone setting in, partially replacing the harsh growl. "You are my human after all... You must behave while you are down here. I must make you listen. " Gaster moved his hand off the human's spine with a slight scratch for punctuation as he conjured a second pair of hands, sending them up the human's legs, grasping at her panties to pull them down to the ground with a yank.

"Aaaahh!" The human yelped out, blood instantly flooding into her cheeks as she wiggled against the hands holding her up, trying desperately to break free. It was no use though, Gaster's magic was too strong, and they only grasped tighter the more she fought against them. "Gaster, please-!"

"I said be quiet, didn't I? I told you to _ **listen.**_ Maybe I need to make it so you can't talk, hm?" The conjured hands that we holding her up suddenly jerked forward and down, sending the human crashing down. She had only a second to prepare for a harsh landing on her knees, but she realized once that she got down on them that the other pair of hands helped brace her fall. However before she could have a chance to process anything else, her hands were yanked back up, her spine stiffening from the force. As she blinked a bit in the darkness, she suddenly saw a faint purple glow move to the front of her face. She instantly knew what it was, and a shock wave of excitement washed over her body.

Gaster's hand moved to the front of his pants, unbuttoning them, pulling out his throbbing cock which illuminated the human's face in a neon purple hue. "Put this in your mouth human, I don't want to hear you talk right now." He smirked and sighed out gently as she quickly did what she was told, moving his left hand to the back of her head, twisting his fingers into her hair. "Mmmm, that's right, yesss..." He closed his eyes as he felt her tongue go to work, it felt so completely amazing, so warm, so wet. Every time she whimpered lightly or moaned against it, it would send chills down his spine. After a minute or two he began to smell a familiar scent fill the air near the two of them, her heat. He looked down at her, his eyes glowing purple in the darkness as he conjured his last set of hands. They moved down to the front of her nightgown, trailing their fingertips like light claws down the fabric until they reached the edge, slipping underneath the fabric to trail back up her flesh. One hand rubbed in-between her thighs, nudging her to open up in which she eagerly did, and the other moved to her right breast, cupping it firmly, rolling her nipple around in between its chalky digits.

The human groaned deeply onto Gaster's purple member as she felt two fingers slide down her slickened slit, then move gently into her tight but wet entrance. She wanted to part away from it so badly and moan out, but she dared not to speak a word, worried that he might change his mind about her "punishment". In all reality she was enjoying this immensely, the feeling of this monster before her making her seem so helpless, so _naughty_. She knew he was enjoying it too-- holding her in his magical bonds, telling her what to do, she could see now that he liked being in control.

"Now human, unnnggg-" He groaned as he felt his body coming close to the edge. He gripped her hair tighter as she began to suck him harder, faster. "I - hhngg, I want you to listen to me from this point on... Do you understand me? If you don't there... w-will be consequences." He saw the human nod as she worked on him, her eyes moving to his as her tongue swirled around the tip of his head. "G-good. Haa- hnnn- I think I'm going to..." His eyes rolled back and closed as his hips started to buck against her face, shaking as the feeling of release broke over his body. He jerked his hips forward as cum burst out of the tip of his pulsing cock, filling the human's mouth up quickly with his magical liquid.

Unable to take anymore in for fear of choking, she moved backwards, letting his cock spill out from her mouth, ribbons of cum still shooting forth covering her face in a glowing purple sticky substance. The taste in her mouth was nothing like human cum, it was more like the texture of slightly set gelatin, and the taste was almost sweet, though that could have just been her imagination. As she worked on swallowing the gelatinous fluid in her mouth, she groaned quietly and began to grind her own hips against the hand that began to finger fuck her faster. Its chalky thumb began to rub her clit in circles, and she looked at Gaster pleadingly as she desperately tried to keep her mouth shut against her own involuntary moans.

As he panted heavily, he looked down to her, the purple lights in his eyes illuminating his face just enough so the human could see his smirk. "Now it's your turn for being a good human and listening to me. Now you may speak. Let your body go, give in, _**submit.**_ "

His last words were like a key that unlocked a chest, the moment he spoke them her body began to shake against his conjured hand that continued to ram into her quaking mound. With a high pitched squeal slipping past her throat she jerked her head back and unleashed, invisible electricity coursing through her body as waves of pleasure crashed upon her in tune with the beat of her heart. As she came a flood of juices spilled forth, dripping down her legs, pooling between her shaking form on the ground in soft sounding drips. When her panting began to subside from her orgasm and her brain began to come back to reality, she felt the hands tug up on her body.

"Get up, we aren't done here yet. At least, I'm not done with you." Gaster hummed as he released the hands above her head and had the other sets of hands helped her up onto her rubbery legs. "Go over to the bed, now, and take off your clothing."

Slowly she once again did as she was told, removing her nightgown, sitting down on the bed swinging her body around to lay flat on her back. She looked to her side to see Gaster make his way over to her since his eyes and groin were still illuminated with his amazing magic. Her eyes followed his as he stood beside her, smiling as he looked down over her now naked form.

"Ahhh, so beautiful... Your flesh, your form, it's all so perfect and I want it to be all mine." His hands cupped her face as he bent down slightly to get a better look at her, brushing her hair out of her face gently.

As he got closer to her she could see something she had never seen before, a very faint glowing in his chest. Hesitating for a moment, she whispered, "Gaster?"

"Yes?"

"Your... chest..."

He looked down and smiled brighter, leaning back up, placing a hand on his chest over his breastplate. "Ah yes, that. Do you want to see it?"

The human bit her lip and nodded slowly, not aware of exactly what she was about to see.

Gaster's hands moved down to the midsection of his coat and unfastened the buttons there, shrugging his shoulders back to let the long back garment fall to the ground. The object in his chest glowed slightly brighter now that the black fabric wasn't hindering it, but his white ribbed turtleneck still hid the vast majority of the object beneath the fabric. His bony hands grasped the bottom of the turtleneck and casually pulled it up, exposing his skeletal form in front of her.

The human gasped as she saw the glowing object fully now, a neon purple heart that seemed to float inside his rib cage, pulsing gently with a steady beat. "Wha-?"

"What is it? It's my soul. All monsters have one. All humans do too, but yours is different from ours, it takes a special kind of magic to see or expose it. Do you know what color soul you have? Pink, and I think it suits you well." Gaster said as he climbed on top of the human, placing his body between her. He picked up her legs gently and placed them on the sides of his hips which were partially exposed from the pants he wore.

The soul in Gaster's chest was glowing so brightly that the human below him could see his entire form exposed for the first time, and as she looked over every inch of him, she blushed a deep shade of vermilion. She knew he was a skeleton monster, but it never really hit home until just now, given that she was able to see right through him. She reached up and gently placed the palm of her hand to the front of his rib cage near where his soul beat, enticing a soft moan to escape from his mouth as her fingers moved to trace along the smooth texture on one of his ribs. She had wondered if his bones were sensitive, and clearly they were, as she could see his expresion grow softer with each section she fingered over. She brought her other hand up to his rib cage as well, wrapping all her fingers into his bones, pulling him down closer to her.

Gaster gasped at the feeling and moved in towards her motion, pressing his bare ribs up against her soft bare flesh. The feeling made him swoon, it was all so wonderful to feel her body so close to his. Wanting to get even closer he reached down, grabbed his throbbing purple length, and lined it up against her wet and ready opening. It only took a minimal amount of effort to push his hips in forward to make it go in, her insides already slick with the juices she spilled for him only minutes earlier. As he began to pump into her, he moaned at the feeling of being inside her once again, and the human moaned alongside him, her fingers stroking and playing with his sensitive bones. He felt the magic in his body pulse stronger as he continued to thrust into her, attempting to get as much of it into her as he could, feeling her tight insides squeeze him as he pulled in and out.

The human moved her hands to his clavicles and gripped onto them tightly, grinding her hips against his in a steady rhythm, feeling herself come close to her breaking point. "Gaster," she spoke breathlessly, "This time, I want you to cum inside me, would you please do that for me?"

Gaster looked down at her and blinked in a slightly confused way, not quite initially understanding what she was talking about until it processed in his mind." Cum? I-inside you? Are... are you sure? If I do that you'll... you'll be marked. You will completely be mine."

"Yes, please... I want to- I want to be yours. I want feel you. I want to feel you quake inside me as you climax. Please..."

"A-alright..." Gaster moaned, his eyes closing as he began to thrust into her at an inhuman speed, arching his hips up slightly at each thrust, hitting a spot deep inside her core. The human's hands moved up to hold on to the vertebrae on his neck and he suddenly couldn't contain his excitement any more. His soul was practically blazing in his chest at this point, and his jaw clenched tightly as he grunted against the human, his body beginning to shake violently. All at once, in a flash of purple light, he yelled out, his eyes snapping open, blazing purple as if on fire. Thick ribbons of purple cum erupted from the tip of his pulsing cock, pumping into the human, filling her up as she requested. As he shuttered against the feeling of her tight walls squeezing around him, he realized that she started to shake as well, so he mustered up all the energy he could and kept pumping into her, sending her into a fit of screaming ecstasy. They both rode their orgasms together, moaning and panting at the feeling of each other.

As things began to subside, Gaster's magical member faded out from view and he moved to the side of the sweaty human, brushing her hair out of her face once again. He traced his phalanges down arms and placed his head on her chest, listening contently to her rapidly beating heart.

The human sighed contently and placed her hand on his skull, encouraging him to listen, as now her heart, and soul, beat only for him.

"Ahhh human, I think... I think I may be able to tell you a story now. But, let us wait until the morning. Let us just enjoy each other for now." Gaster purred as he held the human in his bony arms. He felt her nod and settle in against his body, her warmth making him smile. As the light in his soul grew duller, he closed his eyes and did something he had not done in quite a long time... sleep soundly.

 


	5. Reprieve

**Summary for the Chapter:**

> Emotions begin to bloom, and Gaster feels it is time to open up to the human.

**Notes for the Chapter:**

> (This chapter is a shorter chapter, nothing too nsfw in it save for showering skeletons XD. Enjoy!)

Gaster woke early to find the human sleeping soundly in the bed that they shared overnight. Not wanting to disturb her he did his best to try to move quietly as he got up from the bed. Grabbing his coat and turtleneck off the floor where he had discarded it in their heated passion, he made his way through the darkness to the door. Fortunately he knew his Followers wouldn't be around until he actually summoned them, so he had no worries about running into one awhile he left the human's room in such a state of disarray. As he opened the door, he heard the human stir, the light from the hallway shining softly over her face.

"Gaster?"

"Shhh," he replied, bringing his finger up to his mouth, "I have to leave for now as I have work to do, but please continue sleeping if you need to. We can talk in a little while, alright? I'll have one of my Followers collect you for breakfast together."

"Mmm-hmm." The human hummed as she drifted back to sleep.

Closing the door, Gaster trailed down the empty halls to his room, deciding it was wise to freshen up before he began working, not wanting his Followers to smell any bit of the human on his bones... at least not yet anyways. Tossing his crumpled clothing in the hamper, he made his way into the bathroom, turning the shower on a full heated blast to steam up the room quickly. After adjusting the heat only slightly he stepped in, sighing in relief as the hot water trailed down his bare skeletal structure, filling his body with a satisfying sense of comfort and warmth. He leaned his body against the wall under the shower head, allowing the water beat on his skull, and began to think about how his day as going to go. He had told the human last night that he was going to tell her a story, the story, but he didn't quite know how to start it.

"How can a human quite possibly understand our history? We are but horrible 'creatures' to most of them, they know little of us and... No, I am over thinking this too much. It's not like I am addressing the entire human nation on this, it's just one human, and as willful and... curious as she can be, I think she will be able to grasp it, at least somewhat."

Reluctantly Gaster turned the shower off after spending some time in the blissful heat, grabbed a towel, and made his way back into his bedroom. Toweling off his dripping bones, he made his way to the closet, grabbing a fresh white lab coat, cream colored turtleneck, and black pants. It would hopefully be a few hours before the human would wake up, and he had so much work to do at the Core, so he hastily got dressed . He tried his best to push the thoughts of the human out of his mind, as there wasn't any time for that now, but he kept tracing back to her as he slid his limbs into his clothing. The way she looked, smelled, tasted...

"No, later. Not now." He muttered to himself as he finished getting dressed. He glanced longingly in the direction that the human's room was, wanting to go back to her and feel the heat of her body against his, but he shook his head and made his way to the door, clearing his mind for the work that needed to be done.

\----------------------------------

 

Gaster was able to finish most of his daily plans by the time one of his Followers notified him of the human's awakening.

"Good, good. Go get her breakfast ready, and I will join her momentarily. Direct her to... " He paused sightly to think of where the best place would be to have his private chat. " Direct her to my quarters."

"Your room, sir?" The Follower questioned.

"Yes, I have matters to discuss with her. Don't question me about it again."

The Follower startled slightly at the abrasive tone of Gaster's voice, but he nodded and turned to walk off.

"I'm sorry, please direct her to my quarters." Gaster restated, feeling slightly ashamed for snapping at his Follower.

"Yes, sir." The Follower nodded once again and walked away.

Finishing up the project he was working on, Gaster cleaned up his work area and made his way to the living quarters of the lab where his room resided. As he walked in, he immediately saw that the human was seated there at a table that was set up in the middle of the room, dressed in a simple white gown with thin straps gently resting upon her shoulders. The sight of her was almost too much to bare, and he could feel his face begin to flush as he thanked his Follower for the meal and dismissed them.

"Mind if I take a seat?" Gaster asked as he walked up to the table, staring down at the woman in front of him intensely.

"Please, and there's no need for formalities anymore I would imagine."

Gaster laughed ethereally and sat down "I suppose you are right. We are a bit beyond that point, aren't we?"

The human nodded and looked down at her meal, a soft blush dancing across her cheeks. They both sat in silence for a few moments as she poked at her food, eggs and toast as per usual, until Gaster finally cleared his throat and spoke up.

"So, I said I had a story to tell you if you care to hear about it. The story is about the History of Skeleton Monsters, which I am now willing to share with you since you have shared so much with me... Ahem, about humans, that is."

"I would be honored to hear it." She spoke softly, looking up to gaze into Gaster's eyes. The moment their eyes locked with each other, she saw the blush in Gaster's face glow brighter, soft purple spreading from eye socket to eye socket.

"Yes, w-well... I guess I should start out with why I am willing to tell you the story. It's in regards to what you saw last night in one of my private rooms. The cylinders. The contents in the cylinders... No doubt you saw them, yes? Those are my..." Gaster swallowed hard and closed his eye sockets, trying to find the right words. "Those are my experiem- no. They are my young, in so few words. My successors."

Gaster held up his hands to show the holes punched through the bone clearly, and the human looked at them intensely as if it was the first time viewing them, despite seeing them nearly every day.

"They were both made from me, from my bones. They had to be, it's the only way for skeletons to create the next generation..." Gaster rested his hands back on the table and continued on with his story...


	6. The History of Skeleton Monsters

**Summary for the Chapter:**

> Gaster opens up to the human about the history of skeleton monsters, and explains the contents in the cylinders.

**Notes for the Chapter:**

> This chapter is completely SFW! Ahhh this has been in my head for so long! I hope you enjoy my interpretation and explaination of skeleton monsters within our history!

"For many centuries skeletons and humans lived together above ground, but of all the different types of monsters, humans were always afraid of skeletons, mostly because of our similar nature in appearances, albeit one major obvious difference, flesh. Due to this, skeletons were often depicted as beings of death, "the living dead" as some people would call us, but that terminology is far from the truth, as we are more like beings of life.

You see, in order for skeletons to continue on, we must _**create**_ our next generation, like an artist creates a masterpiece. We can not breed like other monsters can, as we simply do not have the means to do so despite the additional appendages we can manifest should the situation arise. Creation comes in the form of taking a part of ourselves, like a piece of bone, and infusing it willingly with a special form of our magic. We must also take a part of our soul and infuse it with our creation as well, but doing so significantly decreases our possible lifespan. It is an incredibly painful process, and the time it takes for a skeleton to be created is indeed long and arduous, but it is completely necessary if we want to continue on.

Once a skeleton has been created from their maker, they are genderless, and technically remain as such for their entire life cycle. However, most of us choose to take on either masculine or feminine qualities, but it is something we choose in our lives, whatever calls out to us in the long run. Most often though, especially throughout our entire history, skeletons have chosen to take on masculine qualities, though there have been a few notable skeletons with feminine qualities in our history. However, since we technically have no reproductive ability, none of us are truly "male" or "female", even if we refer to ourselves as such, and we can all create the next generation equally.

Another thing about skeletons is we all greatly differ in appearances, it all depends on how we were created. Some skeletons are tall or short, some are small or large. Some of us have bones that fuse together differently, creating more of a solid mass, or even just a few bones here and there. Our skulls also greatly differ, some of us are able to move our bones with magic to create facial expressions, but some skulls almost seem fixed in place, their magical ability allowing them to talk almost telepathically. But nothing is right or wrong, no appearance is better or worse than any other, and we all operate in the same way... with magic."

Gaster pauses for a moment, taking time to pour himself a cup of coffee, drinking it quickly despite the steam coming off the top of the liquid. He sets the mug down, sighs, and looks to the human with a weak smile.

"Magic... As you have seen it does many things for us, but each one of us has a completely unique and original type of magic within our souls. No two skeletons are completely the same when it comes to their magical ability, and it does make certain things hard for us, like trying to explain our abilities to our creations, or help our creations with their abilties. I was made with the ability to create phantom hands, that of which I have used to my advantage my entire life to help me build and create. It is incredibly useful to have an extra set of hands, three extra sets to be exact, and it certainly makes it so I don't have to have many helpers in my laboratory. With my magic I have been building the inside of the Core practically by myself, save for a few other monsters that help in areas that I can't, but it has all been incredibly strenuous, and I recently started to feel a certain emptiness in my life with having no one around but myself and my Followers.

It was in my loneliness that I decided it was finally time to create, but I am not one to make the minimal effort on things. Oh no, I always wanted to do more, create more, and so I did.

I started off first with my left palm. Why my palm you may ask? Well I figured if something happened to my hand in the process, I would at least have my other hands to help me with my work. So, with one of my tools I punched out a part of my bone, an immensely painful process mind you, but luckily for me it was quick. I was left with this hole in my hand, a perfect circle, but I had a great amount of bone to start with, so I worked on getting ready to infuse it with my magic and my soul as soon as I recovered. However a thought came to me during my recovery, why not use my knowledge of science and my ability to build to help the creation process along a bit more? I worked up many plans, and when I finished with the best one I built a cylinder that I could infuse with a constant source of magic to help my creation grow, an environment that was stable enough that I wouldn't have to leave my work behind to focus on constant creation.

As soon as I was ready, I began the process. I infused my bone with my magic, placed a fragment of my soul within it, then inserted it within the cylinder. Afterwards I filled it up with a liquid that conducts magical energy, and started to closely monitor the bone to make sure my magic and soul took to it. It was a very tense initial trial period, and many times the cylinder became dangerously unstable, but after awhile I learned how to balance out the flow of magic, and the bone began to take shape and grow.

After several months of my creation growing steadily, I decided it was time to try again, especially since I felt like my process was more or less worked out. This time I punched my right palm, begun the process over again, and this time I had no close calls as I was prepared to balance things out when they needed to be.

Both of my creations have been growing for over a year now, and I suspect it won't be very much longer before they will be ready to leave their cylinders and grow naturally without the use of artificial environments or a constant stream of magic. I do hope that with this new process of creation that they will be as smart as I am when it comes to science and creation, and they will be able to help me in the laboratory when they become of age."

Gaster smiles stronger now, almost beaming at the thought of such a thing, but then suddenly his smile drops, and his face becomes sullen and sad.

"... I... I won't have much time to spend with them though. Maybe a few years, a decade at best. Punching not just one but two holes from my body and parting with two fragments of my soul will most certainly decrease my lifespan by a significant amount, and I have a feeling they will be left to live most of their lives without me in it. But I will teach them all they will need to know while I can, and hopefully every moment I will be able to spend with them will be one we will all treasure and grow from."

A single purple tear rolled down Gaster's uncracked cheekbone as he clears his throat, trying to clear away the wavering sadness within his voice. He looks to the human slowly, noticing that she had begun to tear up as well.

"I'm sorry, I didn't mean to make you sad. It's just how things are."

Standing up suddenly, the human moved around the table, and walked over to Gaster. She stood in front of him for a moment, holding her arms together across her chest in a look of defense. He looked at her with a puzzled expression on his face, and gasped in surprise as she threw her arms around him, hugging him tightly. Slowly Gaster closed his eyes at her embrace, and wrapped his arms around her softly, resting his head onto her shoulder. He could feel her sob into his coat, and he rubbed her back in an attempt to bring her peace.

"My ... My sweet human, please don't cry for me. This was my choice, I did this willingly, and I knew what the consequences were going to be. I'm not going anywhere any time soon, I'll be here for them, and for you, for as long as I possibly can. We can all be together, if that's what you desire."

Nodding into his chest, the human began to calm herself, and slowly pulled away from Gaster's arms. She wiped her tears, gave him a smile, and placed her hand on top of his, tracing his phalanges with her fingertips.

"I would like nothing more than to be with you."

Gaster's smile returned as he placed his other hand on top of hers. "That makes me so happy. I'm tired of feeling so alone..." Standing up from his chair Gaster pulled the human onto his body, tilting her chin up to look into his eyes. He stroked his hand against her soft cheek, moving up into her hair to cup the back of her head, then leaned down to kiss her softly.

A knock suddenly broke the blissful silence between them, and Gaster growled as he parted away from the human, making his way to the door. He opened it up swiftly and looked at one of his taller Followers with narrowed eyes.

"I had said I didn't want to be disturbed."

"I'm sorry sir, but I have this letter from the King. His carrier asked me to give it to you right away." The tall Follower handed over the letter, and exited away from the door, briefly looking past Gaster to see the human standing in the middle of the room.

"The King, hm? Thank you." Gaster shut the door and opened the letter immediately, his eyes moving swiftly back and forth as he read over the contents. Without warning a short single laugh rang out from him, and he waved the letter around in the air. "Well then, it appears I'm not the only one with "next generation" news today. I'm happy to tell you that the King and Queen just had their first child today, a boy named Asriel! This is indeed great news for the Underground! Hopefully with the birth of this new generation, things will begin to change down here. With any luck, Monsters' lives will start to change." Gaster beamed proudly as he clutched the letter to his chest, but somehow his voice seemed hollow and unbelieving of his own words.

Only time would tell...

**Notes for the Chapter:**

> I tried to write a proper ending for this story, but all conclusions ended too sadly for me to publish. So, as such, this is the end to my first fanfiction ever. I had meant to end it earlier, but this chapter just felt so good at the time. I hope you did enjoy my story though that was originally meant to only be a one shot... I had fun writing it.
> 
> If you like what I do, please let me know! Kudos are greatly appreciated, as well as Follows on my Tumblr at http://esperaqua.tumblr.com/ (be warned though, I do post NSFW stuff on it occasionally). Got a piece of fanart you would like to share of my story? PLEASE, by all means, submit them to me, it would be the ultimate compliment!!!

**Works inspired by this one:**

  * [Human Subject #1](https://archiveofourown.org/works/6425746) by [RedAlaina](https://archiveofourown.org/users/RedAlaina/pseuds/RedAlaina)




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